1. FIELD OF THE INVENTION
The present invention relates to self ballasted lamps and more particularly to a self ballasted lamp that may be flashed during evacuation.
2. DESCRIPTION OF THE PRIOR ART
Heretofore, 160 watt, incandescent parabolic arc reflector lamps had a rated life of 2,000 hours. These lamps utilized a conventional tungsten incandescent filament for providing illumination.
During the manufacture of these lamps, the filaments were energized to incandescent temperatures by the application of increased voltage steps while the lamp was evacuated on an exhaust machine. The purpose of this procedure was to clean the filament and mounting structure and for flashing the filament to a non-sag structure thereby stabilizing the filament. During the initial application of power to the filament, tungsten oxides and other contaminates were vaporized and removed by the exhaust machine. The initial flashing also served to stabilize the filament by forming a large interlocking grain structure in the tungsten which is referred to as a non-sag type of structure.
In an attempt to develope a self ballasted lamp having longer life and improved lumen maintenance, an incandescent filament coil was connected in series with a mercury vapor discharge tube to form a self ballasted lamp. The arc tube included a starter coil which was connected across the arc tube for energization through a bimetallic switch which opened after the arc was struck and the tube heated.
The manufacturing process for this type of lamp had to be modified because of the pressure of the bimetal switch which remained open at the high temperatures required for working and sealing the pyrex glass during the evacuation process. In the high temperature environment, the open bimetal switch prevented the application of intermediate voltage steps to the filament coil and the coil could not be flashed during evacuation of the lamp. Therefore, the coil was flashed after the lamp was removed from the exhaust machine and sealed. This subsequent flashing led to two undesirable results. The tungsten oxides and other contaminates on the filament and mounting structure vaporized and were deposited on the interior surface of the lamp forming a slightly opaque film which reduced the lumen output. In many instances, the vaporized contaminates provided an ion path across the lamp leads which caused the lamp to arc out upon initial lite-up at rated voltage. Thus, the lamps were subject to a short life with early failures, poor lumen maintenance and early blackening of the lamp lens.